This is from personal experience. Something hardly anyone brings up or is ever mentioned is the way that home equity lines of credit show up on your credit report.
Even thought the home equity line is secured against real estate, the home equity line still shows up as "unsecured credit". So how is this bad? "unsecured credit" is credit card debt. I have yet to understand why, but mortgage lenders lump equity lines of credit in with credit card debt, and that is exactly how it shows up on your credit report.
I had never used an equity line to fund an investment purchase until a few years ago. I took an 88k equity line out on one of my homes, thinking this was better then throwing it on lower % credit cards. A year later I was looking to purchase another investment property. My credit score had dropped from 725 to about 670, the only thing that had changed was I had the equity line. I noticed it was showing up as "unsecured credit". I called the mortgage company thinking there was a mistake. Nope, my "equity line" was considered just as bad as credit card debt on my credit report.
I then immediately refinanced that as a 2nd mortgage, my credit score went back up.
This is something that I never hear brought up, and in fact, I have ever asked some lenders and they don't even know this happens...
Long and short, to keep your credit up, don't use equity lines unless you need to, it's no better then having credit card debt on your credit report.